deps: update core dependencies to v1.54.0

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
com.google.api:gax-grpc	minor	1.53.1 -> 1.54.0
com.google.api:gax-bom	minor	1.53.1 -> 1.54.0

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Release Notes

googleapis/gax-java

v1.54.0

Compare Source

02-27-2020 09:07 PST

New Features

• Scale number of threads to scale with number of cpus (#​878)
• Do not shut down executor when WatchDog is shut down (#​871)

Dependencies

• Update google-http-client to 1.34.2 (#​886)
• Update gRPC to 1.27.2 (#​885)
• Update protobuf to 3.11.4 and gRPC to 1.27.1 (#​882)

Documentation

• Add javadoc about being called within single thread (#​856)

Internal / Testing Changes

• Update jacoco to 0.8.5 (#​883)
• Update google format plugin (#​868)
• Set up linkage monitor Kokoro build config for gax-java (#​864)

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